1. Field of the Invention
This invention relates to a quick return mechanism used in a drilling machine for carrying out an automatic feed operation and an automatic quick return operation of the electric drill of the drilling machine.
2. Description of the Related Art
The automatic feed operation and automatic return operation of a conventional drilling machine are performed by changing the rotational directions of a feed motor. The rotational speed of the feed motor is controlled by voltage regulation such that the electric drill is lowered slowly in the feed operation and raised in the quick return operation. However, the speed at which the electric motor can perform quick return is limited when the feed motor is voltage-controlled.
The recent phenomenon of labor shortage has placed a high priority on working efficiency. In this regard, it is desirable that the return speed of the electric drill of a drilling machine after completing drilling work be greatly increased.
The Japanese Unexamined Patent Application Publication No. 1-240210 discloses a quick return mechanism for a drilling machine, which comprises a one-way clutch provided at the input side of a high reduction unit and an engaging clutch provided at the output side thereof. The engagement clutch comprises two clutch pieces each having an inclined surface engaging the other inclined surface. When a predetermined torque is applied, the clutch pieces slide against each other on their inclined surfaces so as to be disengaged from each other. The driving force of the feed motor in the feed operation is transmitted along a different route from that in the quick return operation. Using this arrangement, therefore, the above-mentioned conventional problem is overcome to some extent.
In this prior art, however, sliding of both clutch pieces is likely to cause unstable operation of the engaging clutch.